The presence of the disease sickle cell anemia illustrates that natural selection does not always eliminate _________ alleles.  

A.  polymorphic
B.  dominant
C.  neutral
D.  recessive


D.  recessive

Biology & Microbiology

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The cell walls of fungi are composed of:

a. cellulose. b. lipids. c. glycogen. d. chitin. e. chlorophyll

Biology & Microbiology

When two frog species, Rana pippins and Rana sylvatica, mate, the offspring die early in embryonic development. This is an example of ___________.

A. Hybrid sterility B. Reduced hybrid fertility C. Mechanical isolation D. Reduced hybrid viability

Biology & Microbiology

Small structure in a cell that performs a specific function is the ___________.

Fill in the blank(s) with the appropriate word(s).

Biology & Microbiology

An operon is

a. a gene cluster transcribed as a single mRNA. b. an enzyme responsible for turning genes on and off. c. a site where DNA replication begins. d. a segment of DNA that can move.

Biology & Microbiology